The present invention relates to a holder for an electroconductive unit which is suitable for use in testing printed circuit boards, semiconductor devices and semiconductor wafers by resiliently urging an electroconductive needle member by using a compression coil spring, and a method for making such a holder.
The same applicant previously proposed an electroconductive contact unit assembly comprising a holder consisting of a plate member serving as a support member provided with a plurality of holes, and an electroconductive needle member and compression coil spring received in each hole to simultaneously access a plurality of points of printed circuit boards and multi-pin semiconductor devices for the purpose of testing them or making required measurements (for instance, Japanese patent laid-open publication No. 6-201725). According to this prior proposal, as there is no need to prepare a large number of tubular holders for the electroconductive needle members, it is possible to minimize the pitch of the electroconductive needle members and adapt the electroconductive contact unit assembly to a higher level of densities of the points to be tested.
When such a holder for an electroconductive contact unit assembly is made by drilling holes in a plastic plate member which is electrically insulating, each hole is given with a first section having a large diameter and a second section having a small diameter so that the projecting length of the electroconductive needle member may be defined as required. However, machining work such as drilling is unsuitable for accurately controlling the distribution of the lengths of the two sections in each hole. Therefore, in the case of an electroconductive contact unit assembly having an extremely large number of contact units for testing semiconductor wafers, fluctuations in the projecting length of each electroconductive needle member is inevitable, and there is some difficulty in achieving a uniform and stable contact for all of the electroconductive needle members.
Furthermore, there has been a growing demand for semiconductor devices that can operate in a high temperature environment, and large semiconductor wafers (having a diameter of 200 mm, for instance) are often required to be tested in a high temperature environment. Therefore, the electroconductive contact unit assembly for measuring multiple points of such semiconductor wafers are also required to have a comparable level of resistance to heat and thermal expansion. However, materials having a comparable level of resistance to heat and a small thermal expansion coefficient are relatively difficult to work, and this tends to lower the production efficiency.
To achieve such objects, the present invention provides a holder for an electroconductive contact unit for axially slidably supporting an electroconductive needle member into and out of the holder, the electroconductive needle member including a head portion adapted to contact an object, and an enlarged diameter portion coaxially provided in the head portion and having a larger diameter than the head portion, a compression coil spring being received in the holder for resiliently urging the enlarged diameter portion in a direction to allow the head portion to project out of the holder, characterized by that: the holder comprises a first silicon layer formed with a small hole for coaxially and slidably guiding the head portion, a second silicon layer formed with a large hole for receiving the enlarged diameter portion and the compression coil spring, a silicon oxide film disposed between the two silicon layers and formed with a communication hole having a same diameter as the small hole and coaxial therewith, and an insulating film formed over the inner circumferential surface of the small hole, large hole and communication hole, the projecting length of the head of the needle member being defined by the abutting of the enlarged diameter portion onto the silicon oxide film.
Thus, by using a silicon wafer having a three-layered structure formed by interposing a silicon oxide film with a thickness in the order of 1 xcexcm between first and second silicon layers, a small hole can be formed in the first silicon layer for coaxially and slidably guiding the head portion by plasma etching conducted under condition which would not affect the silicon oxide film, and a large hole can be similarly formed in the second silicon layer for receiving the enlarged diameter portion and the compression coil spring. Also, a communication hole coaxial with the small hole and having a same diameter as the small hole can be formed in the silicon oxide film by plasma etching under a condition which would not affect the silicon layers. The silicon oxide film serves as a stopper by abutting the enlarged diameter portion of the needle member. Therefore, by finishing the surface of the first silicon layer by lapping or the like, the projecting length of the electroconductive needle member can be defined at a high precision.
The projecting length of the electroconductive needle member can be defined at a high precision also by providing a holder for an electroconductive contact unit for axially slidably supporting an electroconductive needle member into and out of the holder, the electroconductive needle member including a head portion adapted to contact an object, and an enlarged diameter portion coaxially provided in the head portion and having a larger diameter than the head portion, a compression coil spring being received in the holder for resiliently urging the enlarged diameter portion in a direction to allow the head portion to project out of the holder, characterized by that: the holder comprises a silicon oxide layer formed with a small hole for coaxially and slidably guiding the head portion, a silicon layer formed with a large hole for receiving the enlarged diameter portion and the compression coil spring, and an insulating film formed over the inner circumferential surface of the large hole, the projecting length of the head of the needle member being defined by the abutting of the enlarged diameter portion onto the silicon oxide layer.
If the insulating film is formed by a silicon oxide film, the insulating film can be easily formed on the inner circumferential surface of the holes of the two silicon layers by forming a silicon oxide film in the presence of oxygen gas.
If the enlarged diameter portion consists of a radial flange portion, and a stem portion projects from the head portion oppositely from the radial flange portion, the large hole being dimensioned so that the stem portion contacts the compression coil spring as the compression coil spring curves under compressive deformation, an electric signal that is required to be exchanged between the head portion of the electroconductive needle member and the compression coil spring can flow axially along the stem portion up to the point of contact between the stem portion and the compression coil spring, and this contributes to the reduction in the electric inductance and resistance because the electric current is not required to be passed through the compression coil spring along a spiral path.
The present invention also provides a method for making a holder for an electroconductive contact unit for axially slidably guiding an electroconductive needle member into and out of the holder, the electroconductive needle member including a head portion adapted to contact an object, and an enlarged diameter portion coaxially provided in the head portion and having a larger diameter than the head portion, a compression coil spring being received in the holder for resiliently urging the enlarged diameter portion in a direction to allow the head portion to project out of the holder, characterized by the steps of: preparing a silicon wafer having a laminated structure including a first silicon layer, second silicon layer and silicon oxide film which is disposed between the two silicon layers; forming a small hole in the first silicon layer for coaxially and slidably guiding the head portion, and a large hole in the second silicon layer for receiving the enlarged diameter portion and the compression coil spring; forming a communication hole coaxial with the small hole and having a same diameter as the small hole in the silicon oxide film; and forming an insulating film over the inner circumferential surface of the large hole, small hole and communication hole.
Thus, by using a silicon wafer having a laminated structure including a first silicon layer, second silicon layer and silicon oxide film which is disposed between the two silicon layers, and forming a communication hole in the silicon oxide film, the projecting length of the electroconductive needle member can be defined at a high precision by the enlarged diameter portion received in the large hole abutting the silicon oxide film.
By forming the holes in the silicon layers by plasma etching conducted under a condition which would not substantially affect the silicon oxide film, the hole forming work can be conducted at a high precision comparable to the level of precision of the mask for the plasma etching. Also, because the depth of the hole is defined by the silicon oxide film, the pitch of the holes, the diameter and depth of each hole can be controlled at a high precision in the order ofxcexcm when a plurality of such electroconductive contact units are arranged in parallel to each other.
By forming the communication hole by plasma etching conducted under a condition which would not substantially affect the silicon layers, the communication hole can be formed in the silicon oxide film both easily and at a high precision.
By conducting the plasma etching for forming the communication hole from the side of the small hole, the communication hole having a same diameter as the small hole can be formed at a high precision.
Other features and advantages of the present invention will be described in the following with reference to the appended drawings.